This invention relates to cooperative identification systems in which the identifying agency and the object to be identified cooperate in the identification process according to a prearranged scheme. More specifically, the invention relates to systems consisting generically of an interrogator-responsor (or "reader") inductively coupled to a transponder (or "tag") where the reader is associated with the identifying agency and the tag is associated with the object to be identified.
Such systems are being used or have the potential of being used for identifying fish, birds, animals, or inanimate objects such as credit cards. Some of the more interesting applications involve objects of small size which means that the transponder must be minute. In many cases it is desirable to permanently attach the tag to the object which means implantation of the device in the tissues of living things and somewhere beneath the surfaces of inanimate objects.
In most cases, implantation of the tag within the object forecloses the use of conventional power sources for powering the tag. Sunlight will usually not penetrate the surface of the object. Chemical sources such as batteries wear out and cannot easily be replaced. Radioactive sources might present unacceptable risks to the object subject to identification.
One approach to powering the tag that has been successfully practiced for many years is to supply the tag with power from the reader by means of an alternating magnetic field generated by the reader. This approach results in a small, highly-reliable tag of indefinite life and is currently the approach of choice.
Tags typically use programmable read-only memories (PROMs) for the storage of identification data to be communicated to readers. The PROMs are programmed either by the manufacturer of the tags at the time of manufacture or by the user prior to implantation in the objects to be identified. Once the PROMs are programmed and the tags are implanted, the PROMs usually cannot be reprogrammed. Thus, tampering with the information stored in a tag is essentially impossible.
There are situations, however, where the user would like to reprogram the tag PROMs in situ because the identification scheme has become known to unauthorized individuals or organizations or certain data associated with the object to be identified needs to be revised or updated. The utilization of reprogrammable PROMs in tags would permit the user to exercise a reprogramming option when the need arose: for example, to store and/or update information which is specific to the object or animal to be identified such as sex, weight, or medical treatment information.
The exclusive utilization of reprogrammable PROMs would, however, prevent the manufacturer from offering after-sale diagnostic and/or warranty services since the tags would no longer have unique and permanent identifying codes.
Thus, the need exists for tags which carry two kinds of information: (1) a manufacturer's serial number and perhaps other data which is permanently associated with a tag and cannot be altered and (2) object-identifying nonvolatile data that is alterable by the user.